Neonatal screening for galactosemia by quantitative analysis of hexose monophosphates using tandem mass spectrometry: a retrospective study.

BACKGROUND: Classic galactosemia (OMIM 230400) is an inherited disorder in the metabolism of galactose caused by deficiency of the enzyme galactose 1-phosphate uridyl transferase (EC 2.7.7.12). Galactosemia leads to accumulation of galactose and galactose 1-phosphate (gal-1-P) in blood and tissues and, if untreated, produces neonatal death or severe mental retardation, cirrhosis of the liver, and cataracts. Hence, the disorder is included in many neonatal screening programs. METHODS: We retrospectively analyzed filter-paper blood samples obtained 4-8 days postpartum for routine neonatal screening from 12 galactosemia patients and 2055 random controls. Total hexose monophosphates (HMPs) were used as a marker of gal-1-P and were assayed by negative-ion mode electrospray tandem mass spectrometry (tandem MS) with settings biased toward gal-1-P detection. The predominant precursor/product ion pair m/z 259/79 was used to quantify total HMPs by external standardization. RESULTS: Linear calibration curves were obtained in the range 0-8 mmol/L gal-1-P. The detection limit was 0.1 mmol/L HMP, and total CVs ranged from 13% at the detection limit to <8% at >1 mmol/L HMP. The method was in agreement with an alkaline phosphatase-galactose dehydrogenase method. All samples from galactosemia patients contained increased HMP concentrations (range for patients, 2.6-5.2 mmol/L; range for reference group, <0.10-0.94 mmol/L). The diagnostic sensitivity and specificity were 100% at a cutoff of 1.2 mmol/L HMP. A Duarte/classic galactosemia compound heterozygous sample could be discriminated clearly from both patient and reference samples. CONCLUSION: Quantitative analysis of HMPs by tandem MS can be used in laboratory investigations of galactosemia.

Design of a pilot study to evaluate tandem mass spectrometry for neonatal screening.

In recent years, tandem mass spectrometry has generated great interest as a method for neonatal screening. The basic principle is electronically controlled separation of analytes by their mass-to-charge ratio. The advantage of this detection system is speed, the capability to analyze for many different compounds in a single analysis, and a minimal need for auxilliary assay reagents. The prevailing screening technique uses stable isotope dilution, butylesterification, and MS/MS analysis to quantify amino acids and acylcamitines in neonatal dried blood spot samples. This allows detection of more than 30 inborn errors of metabolism of amino acids, fatty acids, and other organic acids. In Denmark, a large-scale pilot study is being implemented to evaluate the screening potential of tandem mass spectrometry. National patient registers and medical records from clinical genetics units are used to identify cohorts of healthy infants and infants with selected inborn errors of metabolism. The neonatal screening samples of these infants are retrieved from a biobank and are assayed for amino acids and acylcarnitines using tandem mass spectrometry. This study yields decision values for neonatal screening, which will be evaluated in a subsequent 2-year prospective pilot study, offering the test to 140,000 neonates as a voluntary adjunct to the existing screening program. The organization consists of integrated units for neonatal screening and clinical genetics. The effect of the program will be assessed in terms of screening efficiency, cost and short term clinical outcome.

Technical aspects of neonatal screening using tandem mass spectrometry. Report from the 4th meeting of the International Society for Neonatal Screening.

Quantitative analysis of amino acids (AA) and acylcarnitines using tandem mass spectrometry is an emerging technology used to screen neonatal dried blood spot samples for disorders in the metabolism of AA, organic acids and fatty acids. This paper provides a brief review of some of the technically oriented issues which emerged at the 4th meeting of the International Society for Neonatal Screening in Stockholm, 1999. The information covers sample preparation, instrumentation, data acquistion modes, internal standards, interpretation, confounding factors and practical screening experience.

Cuticular proteins from the giant cockroach, Blaberus craniifer.

The extractable proteins from selected cuticular regions of nymphs and adults of the cockroach, Blaberus craniifer, have been compared by two-dimensional gel-electrophoresis. Only minor differences in protein patterns were observed when nymphal and adult pre-ecdysial cuticles (presumptive exocuticle) were compared, whereas the pattern obtained from nymphal mid-instar cuticle (mainly endocuticle) differed markedly from that obtained from mature adult cuticle. The pattern obtained from nymphal mid-instar cuticle depended upon the specific cuticular region analysed, but the differences within a stage were, to a large extent, quantitative and not qualitative. Seven nymphal endocuticular proteins have been purified to near homogeneity, and the complete amino acid sequence has been determined for three of them. One of the proteins, Bc-NCP1, contains a 16-residue motif repeated three times and containing a disulphide bridge. Protein Bc-NCP2 has a twice repeated motif in common with a pupal protein from Bombyx mori, and Bc-NCP4 contains a twice-repeated sequence of nine residues and is moreover characterized by an unusual high content of valine (22.0%). None of the protein sequences shows significant similarities to the sequences determined for locus endocuticular proteins, except that they all have pyroglutamate as the N-terminal residue.